1010
COMMUNICATIONS TO
The cyclization described in this Communication is of interest in gaining further understanding of Arl participation. Moreover, IV is quite suitable for the further construction of ring A of many natural products. The introduction of a ketone group a t Clo2band the construction of ring As are now in progress.g.I0
THE
EDITOR
Vol. 83
form dimers slowly on ~ t a n d i n g ' , ~we , ~ Jhave considered this possibility in our case. Therefore, the structures considered for the interpretation of the spectrum are the monomer I, the chain dimer 11, and the cyclic dimers IT1 and IV.
(8) As an example of a conventional method for this purpose, see: G. Stork, H. J. E. Loewenthal and P. C. Mukharji, i b i d . , 78, 501 (1950). (9) The author is grateful to Mr. John Carmody for his helpful technical assistance. (10) This investigation was supported by a grant (RG-664G) from the National Institutes of Health, Public Health Service.
I
Me = CH, P h = C,H,
DEPARTMENT OF CHEMISTRY SATORU MASAMUNE UNIVERSITY OF WISCONSIN MADISON, WISCONSIN RECEIVEDJANUARY 21, 1961
Me" RESTRICTED ROTATION I N AMINOBORANES
I11
Iv
Sir: Structure I1 is ruled out because the two methyl I n a recent publication concerning unsymmetri- groups attached to nitrogen would be non-equivcally substituted aminoboranes of the type R1R2-alent, giving two bands. Structure IV would N B R B R the ~ tentative suggestion was made that have only one kind of methyl group attached to such compounds may exhibit cis-trans isomerism.' boron. An equilibrium between two or more forms This hypothesis was made, in the main, on the basis also is excluded because of the observation of only of the melting points and change of melting points three methyl resonances. Structure I11 is consistof mixtures of constant composition and of their ent with the room-temperature spectrum, but does molecular weights. We are now, on the basis of not afford any explanation of the change of band other observations, in a position to offer definite shape as the temperature is raised. Thus i t is conproof of hindered rotation about a boron-nitrogen cluded that our sample consisted of the monomeric bond, leading to cis and trans conformations. form, I, in the whole temperature interval. We have investigated the proton resonance specOn the basis of the temperature variation, up to trum of (methylphenylamino)-dimethylborane,2 118*,of the separation and shape for the resonances (CH3NCeHs)B(CH&, and find that, a t room tem- associated with methyl groups attached to boron, perature, the two methyl groups attached to boron we make a preliminary estimate of the barrier to are non-equivalent. When the temperature is rotation as 15 f 3 kilocalories per mole; the liferaised above 100' these two groups become magnet- time of the individual molecular states is about ically equivalent as rotation about the N-B bond second a t 100'. evidently becomes more rapid. (4) H. J. Brcher and J. Goubeau, 2. anorg. allgcm. Chcm., 268, 133 The p.m.r. spectrum a t room temperature, ob- (1952). (5) E. Wiberg, A. Botz and P. Buchheit, i b i d . , 868, 285 (1948). tained in a Varian high-resolution n.m.r. spectromOF CHEMISTRY GEORGE E. RYSCHKEWITSCH eter a t 60 mc., shows four distinct peaks: (1) a DEPARTMENT OF FLORIDA WALLACE S. BREY,JR. complex phenyl peak, (2) a single sharp N-methyl UNIVERSITY FLORIDA AKEMI SAJI peak a t 4.15 ppm. to high field of the center of the GAINESVILLE, RECEIVED DECEMBER 12, 1960 phenyl peak, (3) a sharp peak, assigned to one Bmethyl, a t 6.64 ppm. above the phenyl, and (4)a sharp peak, assigned to the other B-methyl, a t A NEW SYNTHESIS OF PEPTIDES 6.92 ppm. above phenyl. No other peaks appear. Sir: Peaks (3) and (4) are seen to be relatively close Carboxylates (RCOO-) react rapidly and together. As the temperature is raised, each of smoothly with 3-unsubstituted isoxazolium salts these peaks broadens and they move closer to- (I), under very mild conditions, to give enol esters gether, finally merging into one a t about 100'; (II).' We now record the application of this reaca t yet higher temperatures this single peak nar- tion as the carboxyl-activating step in a simple and rows. This is the characteristic behavior when the practical new synthesis of peptides. rate of intramolecular rotation varies with temperaR'~OCOR tures. a The molecular weight of (methylpheny1amino)dimethylborane has been determined, presumably H cryoscopically in benzene for a freshly distilled I sample, and indicated a monomeric species.2 Clearly the activating reagent (I) may be varied, However, since some aminoboranes are reported to through specific choices for the groups R', R 2 and (1) K. Niedenzu and J. W. Dawson, J . Am. Chcm. Soc., 82, 4223 (1960). R3,with a view to conferring a special degree of (2) B.P. 6 7 O at 14.0 mm., prepared according to R. Niedenzu and reactivity, or particular physical properties, on the J. W.Dawson, ibid., 81, 6663 (1959). reagent, the activated ester intermediate (11), or (3) J. A. Pople, W. G. Schneider and H. J. Bernstein, "Highresolution Nuclear Magnetic Resonance," McGraw-Hill Book Company, Inc., New York, N. Y.,1959, pp. 218-224.
(1) R. B. Woodward and R. A. Olofson. 1.Am. Chcm. Soc., 88, 1007 (1961).
COMMUNICATIONS TO THE EDITOR
Feb. 20, 1961
Z . - ~ h I pL-Leu.OMe
I
1011 76%, 176.6178' 177.5-178.5°0
NHY Z.L-G~U IL-Val.OMe
I
H I11
IV
the by-product (111) from the reaction of the enol ester with amines. Of several isoxazolium salts so far studied by us, N-ethyl-5-phenylisoxazolium-3'-sulfonate (IV) has proved especially useful. For activation, a protected aminoacid or peptide [exactly 1 mole] , dissolved in acetonitrile or nitromethane containing triethylamine [exactly 1mole] , is added to a suspension of the zwitterion (IV) [exactly 1mole] in the same solvent and stirred, a t 0 ' or a t room temperature, until the reagent has dissolved. For combination, the aminoacid ester hydrochloride or peptide ester hydrochloride [exactly 1 mole], and a n equivalent amount of triethylamine, are added, and the reaction mixture is stirred overnight a t room temperature. For isolation, the solvent is removed ilz vacuo, and further simple operations appropriate to the special characteristics of the product peptide are carried out. I n many cases, the residue may simply TABLE I SCALE:2-4 MILLIMOLES Peptiden
Yield of recrystallized peptide of given m.p our best m.p., and best ljierature m.p.
A. Activation in C H X N at 0' for ca. 1 hr. 2.L-Phe IGly.OEt 93%! 109-110' 109.5-110.5' 109-1 10'. Phth.Gly IG1y.OEt 88%, 193.5-194.5' 193.5-194.5' 194-195'' ZL-LYSIGly.OEt 9570, 90.5-92.5' 91.5-93' 2." 92-93'' 2.L-Phe I L-Leu.OMe BO'%, 106-107' 109-109. 50h Z.L-ASPIGly.OEt* 79'33,186-187' 186-187"
I
I
184-185"'
1 "
2.Gly.L-Phe IGly.OEtC
2.Gly.Gly I L-Tyr.OMe
I
OH 2.Gly 1 Gly.Gly.OEt
2.L-Met 1Gly.Gly.OEt
Z.L-Hypro 1Gly.G!y.OEt
I
OH
SO%, 116.5-117.5'
117-118' 120-120.5'f 84%, 159.5-161.5' 159.5-161 .5" 91%, 167-168' 167-168' 167-168'' S6%, 131.5-133' 132.5-133.5' 13 1-1330m SO%, 145-146' 145-116' 144-145'"
B. Activation in CHZNOZa t RT for ca. 7 min. Z.L-ASP IGly.OEt
I
a"
7775, li2.5-173' 172.5-173.5 ' 173-175'P ZL-GIUIL-Tyr.OMe 75%, 198-199' 197.6-198.5' 198-201 P' NHz OH 2.GlylGly.Gly OEtd 90%, 167-168'g 167-168' 167-168"' 2.Gly DL-Phe 1 Gly.OEt S9%, 132-133' 132.5-133' 132-134'1 a The peptide bond was produced a t the point indicated by a vertical stroke in the accompanying designations. Cf. Section B of this Table. This is the Anderson test [ref. 21 ; in addition to the L-tripeptide, 2.2% of Z.GIY.DLCf.Section A of this Table. Phe.Gly.OEt was obtained. G. W. Anderson and R. W. Young, J . A m . Chem. SOC.,7 4 , 5307 (1952). f J. C. Sheehan and J. J. Hlavka, J . Org. Chem., 21, 439 (1956). 0 J. R. Vaughan, Jr., and R. L. New comOsato, J . A m . Chem. Soc.. 74, 676 (1952). S. S. pound. Found: C, 67.73; H, 6.92; N, 6.72. Leach and H. Lindley, Australian J . Chem., 7, 173 (1954). i Ref. 2 ; the same laboratory reports elsewhere values varyNew compound. ing from 116' to 120' for pure samples. G. W. Anderson, Found:. C, 59.48; H, 5.78; N, 9.51. J. Blodinger and A. D. Welcher, J . A m . Chem. Soc., 74, 5309 (1952). C. A. Dekker, S.P. Taylor, Jr., and J. S. Fruton, J . Biol. Chem., 180, 155 (1949). N. C. Davis h'ew compound. and E. L. Smith, ibid., 200, 373 (1953). Found: C, 57.83; H, 6.84; N, 10.78. PE. Sondheimer 76, 2816 (1954). and R. W. Holley, J . A m . Cltem. SOC., g Using free Gly.Gly.OEt, material of the same quality was obtained in 92y0 yield.
SO%, 185.5-187'
1&3-187' 1s4-185°~
I
I
be triturated with water before recrystallization of the peptide from a suitable solvent. Alternatively the reaction mixture may be distributed between water and a suitable immiscible solvent. In all cases, the removal of the secondary product (111) is rendered especially easy by itswater-solubility. Aspecial practical merit of the method is that the peptides ordinarily are produced directly in a n unusually high degree of purity; frequently a single recrystallization is sufficient to give a completely pure product. Typical results are summarized in Table I ; of particular note, beyond the generally excellent yields, are (i) the very small degree of racemization, as judged by the Anderson test,2 (ii) the use of hydroxyproline and tyrosine without protection of hydroxyl groups, and (iii) the very favorable results obtained with asparagine and glutamine derivatives. N-Ethyl-5-phenylisoxazoliurn-3'-sulfonate(IV) 1m.p. 207-208' (dec.). Found: C,52.48; H, 4.20; N,5.48; 0,25.18; S, 12.611 is a stable, crystalline, non-hygroscopic solid.a It is prepared from 5phenyliso~azole~ by treatment for 30 hours with excess pure chlorosulfonic acid a t 102' [- inseparable molecular compound, m.p. 92.6-92.8' (Found: C, 44.36; H. 2.51; N,5.71; C1, 14.68)) containing 5-(3'-chlorosulfonylphenyl)-isoxazole and 5-(4'(2) C/.G . W. Anderson and F. M. Callahan, J . A m . Chem. SOC.,80, 2902 (1958). (3) The reagent is commercially available from Pilot Chemicals, Inc., Watertown 72, Massachusetts. (4) L. Claisen and R . Stock, Bcr., 24, 130 (1891); the preparation has been much improved in detail.
1012
BOOKREVIEWS
chlorosulfonylpheny1)-isoxazole in 2/l ratio], alkylation of the resulting mixed sulfonyl chlorides in methylene chloride by triethyloxonium fluoroborate,j ready separation, by crystallization from acetone/ether, of pure X-ethyl-S-(3’-chlorosulfonylpheny1)-isoxazolium fluoroborate [m.p. 161162’. Found: C, 36.97; H , 3.22; N, 3.79; S , ( 5 ) H. Meerwein, E Battenberg, H. Gold, E. Pfeil and G. Willfang, J . 9rafil. Chem., 164, 83 (1939).
Vol. 83
9.021, and hydrolysis of the latter by 2 N aqueousalcoholic hydrochloric acid a t room temperature. We wish to express our appreciation of support by the National Science Foundation and the National Institutes of Health. CONVERSE MEMORIAL LABORATORY R . B. ~VOODWARD HARVARD UNIVERSITY R. A. OLOFSON CAMBRIDGE 38, MASSACHUSETTS HANS MAYER RECEIVEDJAXUAKY 13, 1961
m
BOOK REVIEWS ,
I
Graphite and its Crystal Compounds. By A. R. UBBELOHDE, and published in 1959. In these papers the subject immeProfessor of Thermodynamics, Imperial College of diately becomes alive and meaningful. Science and Technology, London, and F. A. LEWIS, The book has been beautifully printed by Vivian Ridlcr of Lecturer in Inorganic Chemistry, Queen’s University, the Oxford University Press. The editing has been someBelfast. Oxford University Press, 417 Fifth Avenue, New what careless, particularly in the failure t o provide suffi217 pp. 16 X 24 cm. ciently descriptive captions for some of the figures, tables York 16, Tu’. Y . 1960. xii Price, $5.60. and illustrations. I n the review copy, the paper varied in color. ;1slight lowering of the standards of the Oxford Press The authors state t h a t “this book aims t o give descriptive is therefore evident. I n any case, one must question t h e access t o current lines of research without attempting defini- value of such a monumental production for a book whose tive treatments where these are considered t o be prema- useful life can hardly be more than five years. ture.” Such a statement disarms criticism since in fact no aspect of the subject can be considered t o have reached PROFESSOR OF CHEMISTRY definitive maturity. The book therefore provides a selec- INDIANA UNIVERSITY WALTERJ. MOORE tive, classified and cautiously annotated bibliography, which BLOOMINGTON, INDIANA surveys the literature t o about the middle of 1959. Little effort has been made t o select significant papers for especially detailed discussion or t o provide theoretical background t o help interpret the topics mentioned. The book is primarily Radiation Pyrometry and its Underlying Principles of designed not t o provide scientific information but t o provide Radiant Heat Transfer. B y THOMAS R. HARRISON, references t o sources of information. Technical Advisor, Minneapolis-Honeywell Regulator The general level of the treatinelit can best be conveyed Co., Brown Instruments Div.; formerly Director of by quoting a typical paragraph. Research, The Brown Instrument Co. ; Physicist, Champion Porcelain Co. ; Associate Physicist, National Bureau A treatment has been proposed alternative t o the tight binding of Standards. John Wiley and Sons, Inc., 440 Fourth theory originally introduced by Wallace (cf. also Yamazaki, 1957). . X Avenue, New York 16, N. Y. 1960. xii 3 . 2 3 4 ~ ~ 16 I n this approach (Slonszewski & Weiss, 1955) a detailed group theory 23.5 cm. Price, $12.00. study of the crystal is made, in order t o obtain the ‘topology’ of the
+
bands. I n view of the large spacing between the layers the interlayer interaction is treated by perturbation theory; this leads t o a model of the energy bands which involves only a small number of parameters to be obtained by experiment. No satisfactory correlation has been found between this model and the value of the absolute mag. netic susceptibility found experimentally (McClure, 1959). In application of this model t o explain the results of cyclotron resonance in graphite (Nozieres, 19>8) much experimental information is reviewed.
The title is admirably descriptive of this admirable book. The author, a n authority on the technique of radiation pyrometry, states his prime purposeistopresenttheinformation needed t o enable engineers t o arrive a t definite answers to questions arising in connection with the use of radiation pyrometers in industry. This he has done notably, but his accomplishment is much greater. To give the theoretical and practical explication of radiation pyrometers and pyThc contents are divided as follows: crystallography, rometry t h a t he does, the author (a) presents and develops physical properties, thermal properties, electron properties concisely and accurately the chief principles and ramificaand band structure, crystal compounds of graphite, magnetic tions of energy transfer by thermal radiation; ( b ) adopts a and electrical properties of the crystal compounds, graphite single, sound and acceptable terminology on the subject, oxide, and chemical transformation of graphite t o volatile which has been rather needed; (c) distinguishes clearly the multifarious concepts of spectral, total and band, and norproducts. The treatment of the crystal compounds of graphite is mal, angular and hemispherical, emittances, absorbtances exceptionally good. In general, the chemistry in this book andreflectancesof bodies, and their interrelationships; and (d) is more adequate than the physics. gives tabulated values of Planck’s radiant intensity funcSince the book is not expensive, we can safely say t h a t i t tions, in a convenient and condensed form. This conipenprovides good value. It may easily save many hours of time dium, although here focused on pyrometer practice, is for anyone in need of a ready reference t o the properties of directly applicable, and sufficient in principle, for the broader graphite and its crystal compounds. On a n y particular universe of radiative heat transfer problems. The mathematics of the subject, and the equations topic, however, the original papers will need t o be consulted. I n order t o make sure t h a t nothing important has been required in pyrometer applications, are concisely and (with missed, recourse t o “Chemical Abstracts” will also be re- appendices) very completely developed. About a half of quired. (This book contains about 600 references, and in the text is devoted t o particulars on different types of py1958 alone “Chemical Abstracts” contained more than 400 rometers and optical systems, including “light-guide’’ pyreferences t o graphite.) The system of placing the rcfer- rometers, and the equations and factors on which their Caliences in the text between parentheses makes the book difficult brations are based. Six tables give data on the emittances of materials, and optical properties of pyrometer lens and t o read for any length of time. A student wishing t o obtain a good idea of the current window materials; twelve tables give calibration data for status of this field would not be advised t o turn t o this book. particular pyrometers, and relative responses resulting with He would d o better t o read some of the papers in the Pro- combinations of differelit lenses and windows; corrections ceedings of the Third Conference on Carbon, held in 1 9 5 for the emittance of objects sighted upon are presented in
